The present invention relates to the control strategies implemented in the computing units of the power trains.
It has a preferred, but not limiting, use on power trains comprising at least a combustion engine and a traction electric machine.
More precisely, the object of this invention a method for selecting the target state of a vehicle driveline connecting at least a combustion engine and/or an electric machine to the wheels of the vehicle by means of a transmission, from a set of states present on the transmission. These states are defined by various combinations of couplers and reduction gears, in order to transfer the torque from the combustion engine and/or from the electric machine to the wheels, over one or more gear ratios.
The state of the driveline can be defined by a combination of couplers and reduction gears that are called upon. The aim of the target state of the driveline is to optimize the operating point of the power train. On a combustion power train, a driveline state can be simply defined by the engagement of a ratio and the position (open or closed) of an input clutch between the engine and the gearbox. On a hybrid power train, the definition thereof is inevitably more complex, since it must integrate the state of an electric machine which can drive the vehicle via the same, or via a different axle, as the combustion engine.
The development of the target state of the driveline seeks a compromise between acoustic, driveability, consumption and pollution control performances. The publication U.S. Pat. No. 8,066,417 describes a method for selecting the transmission optimum ratio on a combustion power train, as a function of some constraints influencing the target ratio, such as the speed of the engine thereof, the minimum and maximum speeds of the engine, the maximum available power on each of the ratios, the power requirement of the driver, and the associated consumption of fuel.
This method does not provide for the management of several energy modes. For this reason, it cannot be transposed onto a hybrid power train, since, for a same desired power, there generally exist several possible distributions of power, between the combustion engine, and the electric motor(s). Moreover, the power of the electric machine can optionally pass through the transmission. The electric (ZEV meaning Zero Emission Vehicle) mode is a new power train state to be considered, just like the combustion and hybrid ratios.
On a hybrid vehicle, other considerations can come into play, in the management of the operating modes and of the transmission ratios. As indicated above, the acoustic behavior of the vehicle depends, among other things, on the distribution between the electric power and the combustion power. The driveability, linked to the performance of the power train, also depends on the charge state of the battery, since only the combustion engine can be used when they are discharged. Finally, the energy management laws, which determine, for each operating point, the distribution of power while complying with the consumption and pollution control constraints, and the target ratio of the transmission, must also take into account the charge state of the battery.
The states of a hybrid vehicle driveline can be defined by a combination of coupler(s) and reduction gear(s) specific to a given vehicle architecture. There are more of these combinations than on a conventional transmission, since they integrate the additional coupling of one or more electric motors driving the vehicle optionally on the same axle as the combustion engine. On a hybrid vehicle, the known methods of development prove to be incapable of simultaneously optimizing the consumption and the pollution control, with the driveability and the acoustics.